Think in scenarios instead of forecasts

Short answer #

RATIOXA does not predict which price or yield will occur. A scenario combines traceable assumptions. Test cautious, central and high values and see whether the decision remains stable.

Important variables #

• Plausible range for each uncertain value
• One change per sensitivity test
• Decision crossover
• Source and date of assumption

Worked example #

Calculate solar at 0%, 2% and 4% annual electricity-price change. If NPV stays positive in all cases, the result is more robust than a crossover near 2%.

Break-even: What changes the result? #

Wider realistic ranges strengthen the stress test. Extreme values without justification do not improve the decision.

Common mistakes #

• Labelling the central scenario a forecast
• Changing many variables together
• Interpreting an implausible crossover

Sources & assumptions

• IEA PVPS — Photovoltaic Power Systems Programme (2026-08-17)
• RATIOXA — Methodology and formulas (2026-08-17)